The present invention is generally related to sand processing apparatus and, more particularly, to apparatus for cleaning sand.
As is well known in the art, vibratory processing equipment has been developed to satisfy a wide range of diverse applications. It is oftentimes the case that a system for handling any of a variety of different materials win include as an integral component a vibratory conveyor. Generally, vibratory conveyors may be used for transporting materials to and through a processing section to a post-processing location.
In one particular application, a vibratory conveyor may find advantageous use in a foundry for conveying metal castings or the like from one point to another after they have been formed. There is another very important need to be able to remove sand molds and sand cores and to thereafter reclaim and recirculate the foundry sand which is typically bonded by a resin to form the sand molds and to make the sand cores used in the molds to create interior voids during conventional production of metal castings. After metal castings have been formed, the sand molds and sand cores must be removed, following which the sand must be reclaimed which has typically been accomplished by using a machine called a shake-out.
In this connection, the shake-out is typically of a vibratory nature and operates such that the moisture and clay bonded type sand is simply shaken loose from the metal castings. Optionally, the sand molds and sand cores using resin bonded type sand may be subjected to hot air for the purpose of causing the resin binder in the sand to break down so that the sand will fall away from the metal castings and core passages. In either case, the sand will typically be collected in the bottom of a chamber for further heat or chemical processing to remove any remaining resin to thereby reclaim the sand which is stored for later reuse.
As shown by Nakanishi, U.S. Pat. No. 4,411,709, it has been known that resin bonded sand molds and sand cores can be removed, and the sand simultaneously reconditioned for re-use, by heating the resin bonded molding sand and core sand at a sufficient temperature to be able to pyrolyze the resin binders in the sand. As explained in Crafton, U.S. Pat. No. 5,354,038, and later in Bonnemasou et al., U.S. Pat. No. 5,423,370, it may be advantageous for this heating to be accomplished by utilizing a fluidized bed of sand particles. In particular, Bonnemasou et al. U.S. Pat. No. 5,423,370 point outs that fluidized beds are useful for removing the sand cores from cast aluminum parts, but it also cautions that, when hot, these cast aluminum parts are such that they cannot tolerate xe2x80x9ceven modest handling.xe2x80x9d
Moreover, while it is known to use heat to reclaim the sand by pyrolyzing the resin bonding material or binder, this poses a seemingly unresolvable dilemma; namely, how to apply sufficient heat for efficient pyrolyzing of the bonding material in a manner achieving significant energy conservation. There is also a related problem in that metal castings must typically be heat treated at a specific temperature which must be controlled within close tolerance in order to avoid damage to the castings while at the same time providing a highly efficient and effective heat treatment environment. While the temperature for heat treating the metal castings may be sufficient for decoring purposes, i.e., for removing the cores that are formed of sand and resin bonding material or binder from the castings to reclaim the sand, that same temperature may not be sufficient to reclaim the sand by pyrolyzing the resin bonding material or binder.
Particularly for aluminum castings, the important competing requirements for (1) efficiently and effectively heat treating the castings in an environment where the temperature is controlled within close tolerance, (2) decoring the castings by removing the core sand therefrom, and (3) reclaiming the core sand for reuse in a manner fully ensuring that the resin bonding material or binder is completely pyrolyzed, may well be best achieved in more than a single stage.
The amount of sand used at a particular location may not be enough to justify the cost of providing on-site sand reclamation. Sand cleaning apparatus located off-site, however, must be capable of processing used sand from a variety of different processes. For example, certain cores may have imperfections or simply may not be needed and therefore are not exposed to heat for curing. During processing in conventional sand reclamation apparatus, this uncured sand becomes cured, forming lumps. The lumps do not break down easily and contain binder which is difficult to pyrolyze during the reclaiming process.
Many types of operations require clean sand. Certain types of sands used in foundry cores, for example, have a relatively high silica content of 90% or more. Silica is often added to the sand to increase the acid value of the sand and to obtain other characteristics desirable for use as foundry cores and molds. Virgin sand, defined herein as sand which is mined from the ground and preliminarily screened and washed, often includes non-crystal le materials which are detrimental to the use of the sand in a foundry. Consequently, pure silica is often added to the sand to obtain the desired characteristics. Silica, however, is receiving increasing scrutiny as a potentially harmful material and, in fact, OSHA regulations are beginning to restrict the handling and use of silica. As a result, use of sand reclaiming apparatus which supplies sand requiring the addition of silica is overly costly and hazardous.
The present invention is directed to overcoming one or more of the foregoing problems while achieving one or more of the resulting objects by providing a unique vibratory sand reclamation system.
It is an object of the present invention to provide an apparatus and system for cleaning sand. It is also an object of the invention to provide such an apparatus and system having a fluidized bed moved by vibratory forces to thereby remove impurities from the sand. A further object of the present invention is to provide such an apparatus which conditions sand for foundry use.
Accordingly, the present invention is directed to an apparatus and system for cleaning sand. The apparatus includes a fluidized bed together with means for vibrating the bed to convey and from an entrance to an exit, from which clean sand is removed. Means are provided for supplying hot sand to the fluidized bed at a point generally near the entrance and means are also provided for removing reclaimed hot sand from the fluidized bed.
In an exemplary embodiment, the system comprises a heated chamber for removing and reclaiming sand, a plenum for providing hot air to the heated chamber, and a sand support surface separating the heated chamber from the plenum. Preferably, a continuous uninterrupted vibrated sand support surface defines a continuous conveying path leading from a sand loading conveyor, to and through the fluidized bed, and then to a sand exit conveyor.
In an alternative embodiment, a plurality of hot gas distribution ducts are provided, each of which preferably entirely span the width of the fluidized bed and have perforated lower surfaces in spaced relation to a bottom surface of the heated chamber. This permits hot gas to be directed into sand that surrounds the distribution ducts. The hot gas will first be directed downwardly, will next penetrate upwardly through the sand between the hot gas distribution ducts causing all of the loose sand to be fluidized.
Other objects, advantages and features of the present invention will become apparent from a consideration of the following specification taken in conjunction with the accompanying drawings.